That still won't work. Unfortunately XWiki is too greedy and completely
takes over Solr, assuming that there's only one XWiki instance and that
Solr serves only one purpose, holding that wiki's data. The best way to
make 3 XWiki instances work is to install a separate standalone Solr
webapp, configure the three cores in it, and then configure each XWiki
instance to use the external Solr engine.